This invention relates to an electro-acoustic device. Electro-acoustic devices for alarm watches are known. They generally comprise an electromagnet, a hammer, and a sound generating member, which could be a glass or crystal or a casing of the watch. Actuated by the electromagnet, the hammer strikes a part of the glass which vibrates at its fundamental frequency. Since this fundamental frequency is quite different from the frequency at which the hammer strikes, the efficiency of the device is rather poor, a great amount of energy being lost. Besides the electro-acoustic device can only generate sound at a frequency corresponding to the fundamental frequency and the harmonics of the glass; thus it does not have the possibility of generating sounds at different tones allowing, for example, to differentiate between two kinds of alarms by two different notes.
An object of the present invention is to correct these drawbacks and to propose an improved electro-acoustic device. To make the performance of such a device satisfactory, the movable oscillating element should not only vibrate at its fundamental frequency and its harmonics, but should be able to oscillate at the frequency produced by the electromagnet. This objective is obtained by the means outlined in the claims herein.
Another object of the invention is to provide an electro-acoustic device able to give a clear and loud enough to be heard sound.
A further object of the invention is to provide an electro-acoustic device able to generate sounds of different tones and to play musical tunes.
Still another object of the invention is to provide an electro-acoustic device where the loudness of the sound can be maximized.